Stirrer-ball mill



Oct. 13, 1970 K. MACQUAT 3,533,566

STIRRER-BALL MILL Filed Dec. 18, 1967 5 Sheets-Sheet 2 v OR km Mac; W12 BY a d 34 fllwlaw ATTORNEYS Oct. 13, 1970 K. MACQUAT STIRRER-BALL MILL ,5 Sheets-Sheet 5 Filed Dec. 18,. 1967 FIG. 3

ATTORNEYS 3,533,566 STIRRER-BALL MILL Kurt Macquat, Massagno, Switzerland, assignor to Automatica S.A., Lugano, Switzerland, a corporation of Switzerland Filed Dec. 18, 1967, Ser. No. 691,646 Claims priority, application Switzerland, Dec. 23, 1966, 18,475/66; Nov. 28, 1967, 16,695/67 Int. Cl. B02c 17/16 U.S. Cl. 241-153 17 Claims ABSTRACT OF THE DISCLOSURE A stirrer-ball mill for the size reduction of fluent granular material, comprising housing means internally providing a substantially cylindrical vertically arranged grinding chamber. A rotatable shaft is substantially coaxially disposed in the grinding chamber, such rotatable shaft being provided with a plurality of substantially radially projecting stirrer elements. At least one substantially horizontally arranged partition member provided with throughflow openings serves to subdivide the grinding chamber into separate compartments. Grinding bodies are located in such compartments, the grinding bodies of each compartment possessing different dimensions than the grinding bodies in any other compartment.

BACKGROUND OF THE INVENTION The present invention relates to an improved stirrerball mill apparatus for the size reduction of fluent granular material and which is of the type incorporating a vetrically arranged substantially cylindrical pulverizing or grinding chamber equipped with a coaxially disposed rotatable shaft from which radially protrude a plurality of stirring elements, and such grinding chamber is further provided with freely movable grinding or pulverizing bodies.

The problem very often encountered in industrial processing is to crush different size granular components contained in fluent material in such a manner that after completion of the size reduction or crushing process there appears a mass of material of practically uniform granular size. The expression fluent material or equivalent terms, as employed herein, should be understood to encompass, for example, powder-like substances, plastic substances, liquids and granulated material, all of which may contain comparatively large particles. These types of fluent materials are known, among others, in the foodstuff, chemical and dye industries.

In general, crushing of their granules takes place in mills, of which one known type is the socalled stirrerball mill. Such mill generally consists of a vertical housing having a circular-shaped cylindrical inner chamber provided with a coaxially disposed rotatable shaft. A portion of the inner chamber of the housing is constructed as a grinding or pulverizing chamber which is bounded at its lower and upper ends by a respective partition wall provided with throughflow openings for the material. In the region of this grinding chamber the shaft is equipped with radial stirring or agitator elements. The stirrer ball mills contains a large number of grinding bodies, preferably balls, in their grinding chamber. As a material for these balls there is selected one having a high specific weight in consideration of maximum pressure and abrasion resistance, and, in addition, it should not produce any physiologically adverse effects if used in connection with foodstuffs.

In the continuously operating stirrer ball mill suitably shaped stirring eleemnts rotate and agitate the material which, in turn, is interspersed with grinding balls. The drive energy of the shaft is transferred to the material being ground. The crushing effect exerted upon the coarsegrained particles of the mass is caused by mechanical force as well as by hydraulic friction. The energy transferred by the stirring mechanism accomplishes the size reduction or crushing within the pressure zones between the individual grinding balls and between the grinding balls and the wall of the chamber. Additionally, from one grinding ball to the other there oftentimes exist substantial differences in velocity, leading to the formation of hydrodynamic zones of shear stress.

It is known that the grinding capacity or efliciency can be increased by reducing the diameter of the grinding balls, in that the required length of time for the grinding process can be shortened. On the other hand, the required minimal diameter of the grinding balls is dependent upon the largest possible existent size of the particles to be crushed in order to even accomplish size reduction or crushing.

No optimal grinding capacity can be achieved if the grinding balls are chosen according to a required minimal diameter. It can be only achieved if the diameter of the grinding balls is reduced in proportion to the size of th particles as that size becomes smaller during the ascending flow of the mass. It was found in practice, however, that if the conventional stirrer-ball mills are filled with grinding balls of variable sizes which are stacked according to their diameter, there occurs an intermixture of the different size grinding balls after only a few hours of operation with a resulting reduction of grinding efficiency. This behavior of the grinding balls was quite contrary to the formerly prevalin-g general belief that the grinding balls by themselves would disperse according to their size throughout the height of the grinding chamber.

One disadvantageous effect which is produced by conventional types of stirrer-ball mills, especially by those with shafts of small diameter, is the tendency of those layers of the mass which are located close to the shaft to climb along the shaft. These layers are only marginally exposed to the grinding process and they move through the stirrer-ball mill essentially without having been crushed or reduced in size. This is, of course, a result which is completely contrary to the desired aim of achieving a uniform size of the granules. Additionally, there often appear thermal problems, depending upon the rotational speed of the shaft and the nature of the material or mass. As already mentioned, since the drive work or energy is transferred in the form of heat from the shaft to the material, the latter may reach a prohibitive temperature, thereby undergo undesirable changes.

SUMMARY OF THE INVENTION Accordingly, it is a primary object of the present invention to provide an improved construction of stirrer-ball mill which effectively overcomes the aforementioned drawbacks of the previously considered prior art structures.

Another, more specific object of this invention is directed to the provision of an improved stirrer-ball mill of the mentioned type which is extremely simple and robust in construction, not readily subject to breakdown, highly reliable and efiicient in operation, and capable of subjecting the fluent material to a substantially uniform size reduction;

Now, to implement these and still further objects of the invention which will be more readily apparent as the description proceeds, the stirrer ball mill according to the invention is generally manifested by the features that the grinding chamber is subdivided by at least one horizontal partition device or member equipped with throughflow openings, and that the grinding bodies in each subdivision or compartment have different sizes.

In this manner it becomes possible to separate the grinding process into several functionally different operations. In connection therewith, the grinding bodies become successively smaller in the successive subdivisions or compartments, preferably in the direction of the throughfiow of the material in the mill. This technique makes it possible to approach the optimum grinding capacity hitherto unattained, in that it is possible to choose the grinding bodies for each subdivision or compartment according to the size of the particles of the mass found therein and to clearly keep separated from one another the selected grinding bodies of different dimensions.

According to a preferred embodiment of inventive ball mill, there is employed a shaft whose diameter is at least one-third the diameter of the grinding chamber. This means, however, that with the same number of revolutions of the shaft and the same diameter of the grinding chamber, the shaft attains a higher peripheral velocity, thereby causing greater differences of velocity and, thus, greater frictional forces in the layers of material which coaxially surround the shaft. It also means that a greater centrifugal force of the particles located on or near the surface of the material can be achieved. If the friction and the centrifugal force are sufficiently great, the release loosening of these layers from the shaft and their flow into the grinding process can be substantially improved. It was also found that the frequency of such release or loosening considerably increases with increasing shaft diameters, especially with diameters in excess of one-third of the diameter of the grinding chamber. By reason of the loosening of the material from the shaft and its flow into the grinding process, the directional flow of the mass along the surface of the shaft can be avoided, and thus, there can be achieved a very homogenous mass.

Another advantage of the relatively thick shaft is its large surface which may be directly utilized as a cooling surface by mounting a cooling pipe into the wall of the shaft. This measure allows for a good regulation of the temperature of the mass during the grinding process.

According to a still further variant construction of inventive apparatus, the grinding chamber is provided with at least one subdivision or compartment which does not contain any grinding bodies. This compartment or subdivision may be placed between grinding compartments having grinding bodies of different dimensions and may be connected with pipes leading to the outside.

In this manner, it is possible to reduce the viscosity of the mass by mechanical treatment with the size reduction or crushing itself absent, such mechanical treatment to take place between the individual grinding stages wherein grinding bodies of different sizes are employed. Furthermore, by virtue of this arrangement the mass may be also aerated through its distribution over large surfaces or any other desired substances may be added to the mass between the individual grinding stages.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood, and objects other than those set forth above, will become apparent, when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein:

FIG. 1 is a longitudinal sectional view of a conventional stirrer-ball mill with inlets and outlets and a driving arrangement;

FIG. 2 is a longitudinal sectional view depicting the grinding chamber of a stirrer-ball mill designed according to the teachings of the present invention;

FIG. 3 is a fragmentary view depicting details of a friction slot for closing the lower and upper ends of the grinding chamber; and

FIG. 4 illustrates the subdividcdor compartmentized 4 grinding chamber of a stirrer-ball mill designed according to a preferred embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Describing now the drawings, FIG. 1 illustrates a stirrerball mill of known construction consisting of a grinding chamber or compartment 12 which is surrounded by a cylindrical wall 11. The grinding chamber 12 is closed off at the bottom and top by a respective partition member 17 and 18, for instance apertured partition walls, which allows passage of the material to be ground. A shaft 16 is placed in the interior of this grinding chamber 12 and to which are attached radially extending stirring or agitator elements 14. These stirrer or stirring elements 14 are distributed over the entire length of the shaft 16, yet for the sake of clarity only six such stirrer elements are illustrated at the lower part of the shaft 16. These stirring elements 14 may be in the shape of circular disks which extend from the shaft 16 into the grinding chamber 12, and they may extend close to the housing wall 11. However, they can also be short and may be attached at the same level as the rings 14a attached to the housing wall 11, or they may overlap the rings 14'a protruding from the housing wall 11, as shown in FIG. 2 for instance.

The shaft 16 is provided with a respective journal pin 26 and 27 at its lower and upper end. The journal pin 26 at the lower end is guided in a bearing 26a arranged in the bottom compartment or region 25, whereas the upper journal pin 27 is connected with a suitable transmission 15 through a bearing 27a placed in the upper closure region or compartment 28. Transmission 15 serves to connect the shaft 16 with a suitable non-illustrated drive motor. The bottom region or compartment 25 conically narrows in downward direction and is connected with a three-way valve or cock 29. The upper closure region or compartment 28 is connected with conduit or pipe 19 which leads off the ground material or mass. This outlet pipe 19 incorporates a branch line 19a which also connects with the three-way valve 29.

The third connection with the three-way valve 29 consists of the conduit or pipe 10 which serves for the infeed of the material to be ground. Infinitely variable feed pumps 21 and 20 are arranged at the feed pipe 10 as well as the outlet pipe 19. Pumps 21 and 20 serve to respectively feed the mass to be ground into the mill and to lead it away. The three-way valve 29 can be set in such manner as to permit continuous throughfiow or a closed circulation, whereby in the latter instance the material is circulated several times through the mill. In the grinding chamber 12 and between the stirring elements 14 there are placed grinding bodies, for instance in the shape of balls 43, 44 and 45 of the type shown in FIG. 2, and which move freely between the stirring elements 14. These balls 43, 44 and 45 are preferably formed from steel or hard ceramic.

The grinding compartment or chamber 12 shown in FIG. 2 possesses the inventive separation or partition devices 17a, 17'a. These partition devices 17a and 17a are here shown as substantially ring-shaped disks provided with throughfiow openings or apertures 49 and 49, respectively permitting passage of the material or mass to be ground. These disks 17a and 17 'a are attached to the outside housing wall 11 of the grinding chamber 12 and practically touch the shaft 16 without, however, impeding its rotation. The partition members or dividers 17a and 17a subdivide the grinding chamber 12 into three grinding compartments or sections 46, 47, 48. Each grinding compartment or section 46, 47 and 48 contains a certain number of balls 43, 44 and 45, respectively, used as grinding bodies, only some of which are shown for the sake of clarity in illustration.

The partition members 17a and 17'a allow the through- How of the material to be ground, but not the balls 43,

44 and 45 contained in the neighboring grinding compartments so that these balls always remain in the provided compartments or sections 46, 47, 48 of the grinding chamber 12 irrespective of the nature, consistency and fineness of the material or mass. Each section or compartment 46, 47, and 48 of the grinding chamber 12 contains balls of a different size whereby the larger balls 43 are placed in the lowest grinding compartment or section 46, the medium size balls 44 in the intermediate or middle grinding compartment or section 47, and the smallest balls 45 in the uppermost grinding compartment or section 48. On the other hand, the size of the balls 43, 44 and 45 in the individual grinding compartments 46, 47 and 48, respectively, is the same.

According to a preferred exemplary physical construction of the inventive stirrer-ball mill, the entire grinding chamber 12 has a height of 2 meters and an inside diameter of 40 centimeters and carries, for instance, 96 stirring elements 14 in the shape of shovel blades. These shovel blades 14 are arranged radially and axially offset with respect to one another and form a spiral or helical line with twelve turns on the shaft, wherein each turn or convolution possesses eight blades. In addition, these shovel blades 14 are inclined with respect to the horizontal, as can be seen best by inspecting FIG. 3. The spiral or helical line formed by the shovel blades 14 is, of course, interrupted in the area of the partition members 17a and 17'a, and four threads having thirty-two shovel blades are disposed in each of the grinding compartments or sections 46, 47 and 48. Additionally, those shovel blades 14 pointing in the same radial direction are preferably arranged in rows running parallel to the axis of the shaft 16. The housing wall 11 and the shaft 16 are equipped with a double-wall construction, as shown, in order to divert or remove the heat produced during the grinding operation, and to this end it is possible to pass a suitable coolant through the respective areas 11a and 16a thus enclosed by the illustrated double walls.

It is also possible to arrange the shovel blades 14 on the shaft 16, so as to permit them to rotate about their radial axes, as can be particularly seen in FIG. 3. The vertical rows of shovel blades 14 are preferably rotatable independently of one another. Furthermore, it may be advantageous to shape the shaft 16 conically along its axial direction, since then the peripheral or circumferential speed of the shaft 16 is different at different locations in the housing 11, and thus, the forces which are transmitted to the grinding bodies or elements 43, 44 and 45 and to the material bearing against the shaft 16 are also different.

FIG. 3 further illustrates details of the upper closing or partition device 18 constructed as a friction slot 100. This friction slot 100 embodies a substantially circularshaped disk 31 which is attached to the shaft 16 and a sub stantially ring-shaped disk 32 attached to the housing wall 11 in axial spacing from the disk 31. In this embodiment of inventive apparatus, the distance between disk 31 and disk 32 is smaller than the size of the grinding balls in the adjoining grinding compartment.

During operation of the described stirrer-ball mill, a fluent mass is fed into the bottom region or area 25 through an inlet pipe, such as pipe of FIG. 1. In this bottom area 25 which enlarges conically upwards, as shown, the ascending mass spreads practically evenly over the entire entrance area of the grinding chamber 12 separated by the divider or partition wall 17. The mass or material is then pushed upwards, passing through the grinding balls 43, after its entrance into the grinding chamber 12. The shovel blades 14 of the rotating shaft 16 engage these grinding balls 43 and move them intensively, resulting in the comminution or crushing of the material therebetween. On account of the relatively large grinding balls 43 in the lower grinding compartment or section 46, the largest particles contained in the material are primarily reduced in size within this compartment.

The material, having been pushed upwards, then enters the intermediate grinding section or compartment 47 through the aperatured partition wall 17a, where it then comes into contact with the smaller balls 44 which have the same total weight but possess a substantially larger frictional area, so that the mass is further ground in this compartment 47. After passage through the middle grinding compartment or section 47, the mass or material then reaches the upper grinding compartment or section 48 through the partition wall or divider 17a in which there are located the still smaller balls which possess a still larger frictional area although the same total weight. After passage through the upper grinding section 48, the material then reaches the closure or terminal area 28 from where it is withdrawn by the pump 20 into the pipe or conduit 19.

In order to grind a chocolate mass containing 12% cocoa, 24% whole milk powder, sugar and 9% cocoa butter, 350 kilogram grinding balls 43 having a diameter of 12 millimeters can be used in the lower compartment 46, 350 kilogram grinding balls 44 having a diameter of 10 millimeters can be used in the middle or intermediate compartment 47, and 350 kilogram grinding balls 45 having a diameter of 6 millimeters can be used in the upper grinding compartment or section 48. With a rotational speed of the shaft of 150 revolutions per minute and a rate of flow of 12 kilograms of material per minute, the mass which leaves the stirrer-ball mill has an average grain size of 20 microns.

Finally, FIG. 4 depicts an embodiment of inventive stirrer-ball mill containing a cylindrical housing and a shaft 61 arranged concentrically with respect to one another. The cylindrical housing 60 is closed off at its upper and lower ends by closure sieves or friction slots 62 and 63, respectively, as already described in connection with FIG. 3. The bottom area 64 is fed by two conduits or pipes, one pipe 65 bringing in the material to be ground and the other pipe 66 allows the introduction of a suitable treatment medium, as e.g., air, into the material. The upper terminal region area 67 is connected with a pipe 68 which removes the ground and treated mass. The pipes 66 and 67 may be provided with suitable pumps or the like, in the manner previously considered with regard to the construction of FIG. 1. The upper end of the shaft 61 is connected with a suitable infinitely variable transmission or drive unit 70 operated by a suitable electric motor (not shown). The shaft 61 has attached thereto and aligned in vertical rows stirring or stirrer elements in the shape of shovel blades 75, and 75". These shovel blades 75, 75 and 75" form vertical rows which are displaced in the longitudinal direction of the row, that is, displaced vertically with respect to one another. This displacement is selected in such a manner that, if shovel blades are used which are inclined with respect to the horizontal, the lower and upper edges of a shovel blade are disposed at the same height as the upper and lower edges of its neighboring shovel blade. In this manner it is ensured that as the shaft 61 rotates, no horizontal layer will be possible which is not reached by the blades, and that the material fed into the stirrer-ball mill is not only ground, but also positively transported from bottom to top. Furthermore, in the middle or intermediate grinding section or compartment 86, a circular ring-shaped scraper 76 is attached to the shaft 61 between the shovel blades 75', the function of which is to interrupt the How of the marginal layer of material ascending along the shaft 61, and to return this outer layer into the remainder of the material and to permit it to commingle therewith.

The entire chamber enclosed by the housing 60 is subdivided by partition members 80, 81, 82, 83 into five compartments having different functions. Each of these partition members is constructed as a separating or partition sieve. As already described, the respective compartments or sections 85, 86, and 87 which are located between the lower closure 62 and the partition wall 80, between the partition walls 81 and 82, and between the partition wall 83 and the upper closure member 63, are filled with balls of various diameters 51, 52 and 53, respectively. The shaft 61 carries the stirrer elements in the form of shovel blades in the compartment 88 bounded by the partition walls 80 and 81 as well as in the compartments or sections 85, 86 and 87. However, this compartment 88 does not contain any grinding bodies. The section or compartment 89 which is disposed between the partition walls 82 and 83, contains two stirring elements 90 and 91 in the form of substantially circular ring-shaped disks which are attached to the shaft 61. Also, no grinding bodies are located in this compartment 89. Suitable conduits or pipes 95 and 96, which can be closed by appropriate non-illustrated valves, communicate with the lower and the upper regions of the compartment 89, as shown.

During operation, the material to be ground is pumped into the lower section 64 through pipe 65, from where it is moved along a very complicated path to the partition member 80, by means of which it enters compartment 88. As already mentioned, this compartment or section 88 contains no grinding bodies, so that the material can follow unimpeded the rapid movements of the shovel blades and is thereby thoroughly kneaded and mixed. As experience has shown, the viscosity of the mass, especially when dealing with a chocolate mass, can be noticeably reduced in this manner. After passing compartment 88, the mass or material then enters the middle compartment or section 86 through partition member 81 where it is ground further in a similar fashion as in the lower grinding section 85, but with smaller grinding balls 54. The mass then leaves the middle grinding section 86 through partition member 82 and enters compartment 89 which contains no grinding balls. The conduit or pipe 95 introduces air continuously into this compartment 89 which mixes with the mass which is thoroughly agitated in this section or compartment by the stirring elements 90 and 91 shaped as disks. The mass is thus completely aerated, which is again important when the stirrer-ball mill is used in the foodstuff industry. The pipe 96 sucks off the air after it has been charged with undesired gaseous, easily evaporable ingredients which develop in the material or mass during its grinding and kneading. The aerated mass then enters into the upper compartment or section 87 through partition member 83 where it is again ground fine with the aid of grinding balls 53. The mass whose grinding is now completed, having passed through the upper grinding section 87 and departed through the partition member 63, is now withdrawn from the upper terminal or closure area 67 through pipe 68 in order to be treated further or to be immediately used.

It is also possible, of course, to introduce into compartment 89 which has no grinding balls, some neutral, nonoxidizing gas, as for example nitrogen, instead of air. Instead of a gas, there may be also introduced any other treating medium or an additive. Also, the described subdivision of the mill into three grinding compartments or sections 85, 86 and 87 and two sections or compartments 88 and 89 with no grinding bodies, can be accommodated to the particular utilization of the mill, in that for example there may be provided only one compartment or section with no grinding balls or more than two such sections. Finally, the first compartment or section 88 containing no grinding balls can be also equipped with conduits or pipes leading outside in order to introduce treatment media or additives.

The use of the described stirrer-ball mill is not to be considered as limited to grinding of materials which are useful in the foodstuff industry, but it may be used equally Well for fine grinding of inorganic suspensions or solutions as, for instance dyestuffs or plastics in liquid form.

While there is shown and described present preferred embodiments of the invention, it is to be understood that the invention is not limited thereto, but may be practiced within the scope of the following claims. Accordingly,

What is claimed is:

1. A stirrer ball mill for the continuous grinding of fluent granular materials, comprising a plurality of grinding compartments through which said materials are fed in sequence, each of said grinding compartments having therein a plurality of freely movable grinding bodies, the grinding bodies within each one of said compartments having a size range different from the grinding bodies within any other of said grinding compartments, and at least one treatment compartment disposed between two of said grinding compartments and devoid of grinding bodies, said granular materials being further treated within said treatment compartment the grinding stages defined by said two grinding compartments.

2. A stirrer ball mill as defined in claim 1, wherein said treatment compartment includes stirrer means therein for reducing the viscosity of said materials.

3. A stirrer ball mill as defined in claim 1, wherein said treatment compartment comprises fluid supply means for fluid treatment of said materials.

4. A stirrer ball mill as defined in claim 3, wherein said treatment compartment includes inlet means for said materials at one end thereof and outlet means for said materials at the opposite end thereof, said inlet means and said outlet means respectively communicating with said two grinding compartments, and said fluid supply means comprises gas inlet means adjacent to said one end and gas outlet means adjacent to said opposite end, whereby a treatment gas may be introduced to said treatment compartment and entrained in said materials.

5. A stirrer ball mill as defined in claim 1, wherein in each of said grinding compartments, said grinding bodies are larger than in the succeeding compartments relative to the direction of flow of said materials.

6. A stirrer ball mill as defined in claim 5, wherein said treatment compartment has an axial length shorter than the axial length of any of said grinding compartments.

7. A stirrer ball mill for the continuous size reduction of fluid granular materials, comprising a substantially cylindrical grinding chamber having a vertical axis, rotatable shaft means coaxially disposed within said chamber and having secured thereto a plurality of radially extending stirrer elements, said chamber being divided by at least one horizontal partition means into a plurality of grinding compartments, said partition means having through flow openings therein for said materials, a plurality of freely movable grinding bodies within each of said grinding compartments, the grinding bodies within each one of said grinding compartments having a different size from those within the others of said compartments, and at least one treatment compartment devoid of grinding bodies disposed between two of said grinding compartments and having fluid inlet and outlet fluid conduit means communicating therewith, whereby a treatment fluid may be introduced within said treatment compartment and entrained within said granular materials.

8. A stirrer ball mill as defined in claim 7, wherein said treatment compartment comprises two partition members at opposite ends thereof, each of said partition members having through flow openings therein respectively communicating with one of said two grinding compartments, and at least one stirrer element within said treatment compartment between said partition members for reducing the viscosity of the granular materials therein.

9. A stirrer ball mill for the continuous size reduction of fluent granular materials, comprising a substantially cylindrical grinding chamber having a vertical axis, a generally coaxial rotatable shaft disposed within said chamber and having secured thereto a plurality of radially extending stirrer members, said grinding chamber being divided by at least one horizontal partition member into a plurality of grinding compartments. said partition memher having through flow openings therein providing communication between said grinding compartments, a plurality of freely movable grinding bodies disposed within each of said grinding compartments, the grinding bodies within each one of said grinding compartments having a different size from those Within the others of said compartments, and at least one treatment compartment devoid of grinding bodies disposed between two of said grinding compartments and in communication therewith, said treatment compartment having therein means for reducing the viscosity of the fluent mass therein, and fluid inlet and discharge means for introducing a treatment fluid to said treatment compartment, whereby said treatment fluid may be entrained within said fluent material.

10. A stirrer ball mill as defined in claim 9, wherein said treatment fluid comprises air, said fluent materials being aerated thereby.

11. A stirrer ball mill as defined in claim 9, wherein said treatment fluid comprises a treatment additive.

12. A stirrer ball mill for the size reduction of fluent granular materials, comprising housing means providing a substantially cylindrical, vertically arranged grinding chamber therein, a rotatable shaft substantially coaxially disposed in said chamber, said rotatable shaft being provided with a plurality of substantially radially projecting stirrer elements, at least one substantially horizontally disposed partition member provided with through flow openings for subdividing said chamber into a plurality of separate grinding compartments, grinding bodies disposed within each of said grinding compartments, the grinding bodies of each grinding compartment possessing diflerent dimensions from the grinding bodies in any other grinding compartment, and at least one treatment compartment devoid of said grinding bodies and having means therein for the further treatment of said fluent material.

13. A stirrer-ball mill according to claim 12, wherein said at least one compartment devoid of said grinding bodies is provided for the reduction of the viscosity of the material and is formed by at least two partition members attached to the wall of said housing means defining said grinding chamber, at least one stirrer element located in said one compartment between said two partition members. I

14. A stirrer-ball mill according to claim 12, wherein at least some of said stirrer elements are constructed in the form of shovel blades.

15. A stirrer-ball mill according to claim 12, further including conduit means communicating with said one compartment devoid of grinding bodies for introducing or withdrawing additives or treatment media for the fluent, granular material.

16. A stirrer-ball mill according to claim 12, wherein said one compartment devoid of said grinding bodies is disposed between compartments containing grinding bodies of different dimensions.

17. A stirrer-ball mill according to claim 12, further including at least one scraper means attached to said shaft in the area of at least one compartment containing grinding balls.

References Cited UNITED STATES PATENTS 2,578,274 12/1951 Weigham et a1 241-43 X 2,779,752 1/1957 Vining 241-17O X 2,943,800 7/1960 Wultsch 241192 X 3,233,835 2/1966 Sevin et al. 24l171 X 3,311,310 3/1967 Engels et a1. 241171 X 3,337,140 8/1967 Wahl 241-172 X ROBERT C. RIORDON, Primary Examiner M. G. RASKIN, Assistant Examiner US. Cl. X.R. 

